This invention relates to improvements made to a double enveloping worm gear assembly for use in a drive axle.
A typical drive axle assembly includes two wheels driven by axle shafts which are driven by a common differential. Usually, the differential utilizes standard hypoid gearing comprised of a pinion gear and a ring gear with the pinion gear receiving input from a driveshaft. However, other types of gearing such as cylindrical worm gearing have been used in drive axles.
A worm gear assembly includes a threaded worm having at least one thread defined by a thread profile and a worm gear having teeth defined by a tooth profile. For a single enveloping worm gear assembly the top surfaces of the worm gear teeth are curved such that they envelop the worm. For a double enveloping worm gear assembly, in addition to the worm gear teeth being curved, the threaded length of the worm is narrower at its mid-point than at its ends, i.e., it is cured along its threaded length, so that the worm envelops the worm gear.
The thread profile for the worm as used in either a single or double enveloping worm gear assembly has two sides, each having a pressure angle. The tooth profile for the worm gear also has two sides each having a pressure angle. The pressure angles of the tooth profile correspond to the respective pressure angles of the thread profile for proper meshing of the thread with the teeth as the worm drives the worm gear. Typically, these pressure angles are all equal to each other and usually have a standard value of twenty degrees.
Hypoid gearing is significantly more efficient than traditional worm gear assemblies, however, worm gear assemblies have improved packaging capabilities, are lighter, and quieter than typical hypoid gear assemblies. It would be desirable to increase the efficiency of a worm gear assembly without decreasing its other advantages over traditional hypoid gearing.
Hence, there is a need for a worm gear assembly which has improved efficiency and component life, is quieter, has higher torque handling capacity, improved weight savings, and which reduces effect of shock loading when compared to conventional worm and hypoid gear assemblies